The agency began a health inspection in June after receiving information that fires had occurred in the Ohio plant, and that large amounts of dust from the manufacturing process had accumulated throughout the worksite.

"The Occupational Safety and Health Administration will not tolerate the exposure of workers to preventable hazardous conditions," said acting Assistant Secretary of Labor for OSHA Jordan Barab. "The destructive and violent power of dust explosions is clear, and employers have an obligation to keep workers safe."

Following the health inspection, OSHA issued four willful violations with penalties totaling $252,000 and five serious violations with penalties totaling $14,900. The willful violations allege the lack of explosion protection, the failure to equip process equipment with combustible dust collection systems, hazardous accumulations of dust, and the use of electrical equipment that was unsafe to use in areas with combustible dust accumulation. The serious violations address hazards from workers breathing the dust, allowing combustible materials in areas where workers were welding, and unsafe electrical equipment and practices. The proposed health violation fines total $266,900.

OSHA also initiated a safety inspection that resulted in the issuance of two willful violations with penalties totaling $126,000 and 21 serious violations with penalties totaling $80,000. The willful violations allege confined space hazards and failing to train employees in using the fire fighting system. The serious violations allege a variety of hazards. They include fall hazards, problems with emergency exit lighting, failure to train on and exposure to hazardous machine-energy sources, and additional unsafe electrical equipment and practices. The proposed safety violation fines total $206,000.

A willful violation is one committed with intentional, knowing or voluntary disregard for the law's requirements, or with plain indifference to employee safety and health. An OSHA violation is serious if death or serious physical harm can result if an accident were to occur from a hazard an employer knew or should have known exists.

The site in Upper Sandusky, Ohio, then owned by Advanced Organics Inc., has been inspected twice since 2004, with serious citations issued for fall protection, combustible dust issues, electrical hazards, machine guarding, and fall hazards following the earlier inspections.

The safety and health fines total $472,900; the company has 15 business days from receipt of the citations to comply, request an informal conference with the OSHA area director, or contest the findings before the independent Occupational Safety and Health Review Commission.